There is known in the art a classifying device that uses guide vanes to generate a whirling gas stream, which imparts a whirling motion to powder, and centrifuges the powder into fine particles and coarse particles.
In a powder classifying device proposed in Patent Literature 1, for example, there are provided near the lower end of a cone-shaped powder passage a plurality of guide vanes disposed in upper and lower annular stages separated by a partition board. Exhaust air is discharged from an exhaust pipe, generating air circulation passing through the guide vanes. Powder that passes through the cone-shaped powder passage and falls into spaces between the upper guide vanes are caused to gyrate, so that the powder is classified according to the relationship between centrifugal force and drag.
Patent Literature 2 describes a material supply device in which guide vanes are disposed in an annular arrangement around a material supply cylinder and powder material supplied into the material supply cylinder is dispersed by introducing air from the outside through secondary air inlet passages between adjacent guide vanes. Air stream generated by suction and discharge through a discharge pipe causes the material to whirl at high speed in dispersion as it falls down the material supply cylinder, flows into a classifying chamber, and is therein centrifuged into coarse powder and fine powder.
Patent Literature 3 describes a stream-type classifying device comprising guide vanes disposed around a classifying chamber in an annular arrangement and air stream inlet passages provided between adjacent guide vanes, wherein powder supplied into the classifying chamber is caused to whirl at high speed by air suction and discharge through an exhaust pipe and centrifuged into fine powder and coarse powder.